Variable thickness embolic filtering devices and method of manufacturing the same

ABSTRACT

A strut assembly to be used in conjunction with an embolic filtering device has varying strut thicknesses, with the thickness selected based at least in part on the flexing characteristics of the particular portion of the strut assembly. The strut assembly is formed with patterns having flexing portions and stable portions, with the flexing portions contributing to the flexibility of the strut assembly during delivery and recovery in the patient&#39;s vasculature. The stable portions remain relatively unflexed and stiff when being delivered or recovered from the patient&#39;s vasculature. The stable portions provide strength and increased radiopacity to the strut assembly which is needed when the strut assembly is deployed in the body vessel. The flexing portions act much like a mechanical hinges in providing the needed flexibility to resiliently bend when being delivered through tortuous anatomy of the patient.

BACKGROUND OF THE INVENTION

The present invention relates generally to filtering devices and systemswhich can be used when an interventional procedure is being performed ina stenosed or occluded region of a body vessel to capture embolicmaterial that may be created and released into the vessel during theprocedure. The present invention is more particularly directed to anembolic filtering device with a strut assembly having varying wallthickness and strut widths. The present invention is particularly usefulwhen an interventional procedure, such as balloon angioplasty, stentingprocedures, laser angioplasty or atherectomy, is being performed in acritical body vessel, such as the carotid arteries, where the release ofembolic debris into the bloodstream can occlude the flow of oxygenatedblood to the brain, resulting in grave consequences to the patient.While the present invention is particularly useful in carotidprocedures, the invention can be used in conjunction with any vascularinterventional procedure in which an embolic risk is present.

Numerous procedures have been developed for treating occluded bloodvessels to allow blood to flow without obstruction. Such proceduresusually involve the percutaneous introduction of the interventionaldevice into the lumen of the artery, usually through a catheter. Onewidely known and medically accepted procedure is balloon angioplasty inwhich an inflatable balloon is introduced within the stenosed region ofthe blood vessel to dilate the occluded vessel. The balloon catheter isinitially inserted into the patient's arterial system and is advancedand manipulated into the area of stenosis in the artery. The balloon isinflated to compress the plaque and press the vessel wall radiallyoutward to increase the diameter of the blood vessel, resulting inincreased blood flow. The balloon is then deflated to a small profile sothat the dilatation catheter can be withdrawn from the patient'svasculature and the blood flow resumed through the dilated artery. Asshould be appreciated by those skilled in the art, while theabove-described procedure is typical, it is not the only method used inangioplasty.

Another procedure is laser angioplasty which utilizes a laser to ablatethe stenosis by super heating and vaporizing the deposited plaque.Atherectomy is yet another method of treating a stenosed blood vessel inwhich cutting blades are rotated to shave the deposited plaque from thearterial wall. A vacuum catheter is usually used to capture the shavedplaque or thrombus from the blood stream during this procedure.

In the procedures of the kind referenced above, abrupt reclosure mayoccur or restenosis of the artery may develop over time, which mayrequire another angioplasty procedure, a surgical bypass operation, orsome other method of repairing or strengthening the area. To reduce thelikelihood of the occurrence of abrupt reclosure and to strengthen thearea, a physician can implant an intravascular prosthesis formaintaining vascular patency, commonly known as a stent, inside theartery across the lesion. The stent can be crimped tightly onto theballoon portion of the catheter and transported in its delivery diameterthrough the patient's vasculature. At the deployment site, the stent isexpanded to a larger diameter, often by inflating the balloon portion ofthe catheter.

The above non-surgical interventional procedures, when successful, avoidthe necessity of major surgical operations. However, there is one commonproblem which can become associated with all of these non-surgicalprocedures, namely, the potential release of embolic debris into thebloodstream that can occlude distal vasculature and cause significanthealth problems to the patient. For example, during deployment of astent, it is possible that the metal struts of the stent can cut intothe stenosis and shear off pieces of plaque which become embolic debristhat can travel downstream and lodge somewhere in the patient's vascularsystem. Pieces of plaque material can sometimes dislodge from thestenosis during a balloon angioplasty procedure and become released intothe bloodstream. Additionally, while complete vaporization of plaque isthe intended goal during laser angioplasty, sometimes particles are notfully vaporized and thus enter the bloodstream. Likewise, not all of theemboli created during an atherectomy procedure may be drawn into thevacuum catheter and, as a result, enter the bloodstream as well.

When any of the above-described procedures are performed in the carotidarteries, the release of emboli into the circulatory system can beextremely dangerous and sometimes fatal to the patient. Debris that iscarried by the bloodstream to distal vessels of the brain can causethese cerebral vessels to occlude, resulting in a stroke, and in somecases, death. Therefore, although cerebral percutaneous transluminalangioplasty has been performed in the past, the number of proceduresperformed has been limited due to the justifiable fear of causing anembolic stroke should embolic debris enter the bloodstream and blockvital downstream blood passages.

Medical devices have been developed to attempt to deal with the problemcreated when debris or fragments enter the circulatory system followingvessel treatment utilizing any one of the above-identified procedures.One approach which has been attempted is the cutting of any debris intominute sizes which pose little chance of becoming occluded in majorvessels within the patient's vasculature. However, it is often difficultto control the size of the fragments which are formed, and the potentialrisk of vessel occlusion still exists, making such a procedure in thecarotid arteries a high-risk proposition.

Other techniques include the use of catheters with a vacuum source whichprovides temporary suction to remove embolic debris from thebloodstream. However, as mentioned above, there can be complicationsassociated with such systems if the vacuum catheter does not remove allof the embolic material from the bloodstream. Also, a powerful suctioncould cause trauma to the patient's vasculature.

Still other techniques which have had some limited success include theplacement of a filter or trap downstream from the treatment site tocapture embolic debris before it reaches the smaller blood vesselsdownstream. The placement of a filter in the patient's vasculatureduring treatment of the vascular lesion can reduce the presence of theembolic debris in the bloodstream. Such embolic filters are usuallydelivered in a collapsed position through the patient's vasculature andthen expanded to trap the embolic debris. Some of these embolic filtersare self expanding and utilize a restraining sheath which maintains theexpandable filter in a collapsed position until it is ready to beexpanded within the patient's vasculature. The physician can retract theproximal end of the restraining sheath to expose the expandable filter,causing the filter to expand at the desired location. Once the procedureis completed, the filter can be collapsed, and the filter (with thetrapped embolic debris) can then be removed from the vessel. While afilter can be effective in capturing embolic material, the filter stillneeds to be collapsed and removed from the vessel. During this step,there is a possibility that trapped embolic debris can backflow throughthe inlet opening of the filter and enter the bloodstream as thefiltering system is being collapsed and removed from the patient.Therefore, it is important that any captured embolic debris remaintrapped within this filter so that particles are not released back intothe body vessel. Additionally, the recovery apparatus should berelatively flexible to avoid straightening of the body vessel. Recoverydevices which are too stiff can cause trauma to the vessel walls as thefilter is being collapsed and removed from the vasculature.

Some prior art expandable filters are attached to the distal end of aguide wire or guide wire-like tubing that allows the filtering device tobe placed in the patient's vasculature as the guide wire is steered bythe physician. Once the guide wire is in proper position in thevasculature, the embolic filter can be deployed to capture embolicdebris. Some embolic filter devices which utilize a guide wire forpositioning also utilize the restraining sheath to maintain theexpandable filter in a collapsed position. Once the proximal end of therestraining sheath is retracted by the physician, the expandable filterwill move into its fully expanded position within the patient'svasculature. The restraining sheath can then be removed from the guidewire allowing the guide wire to be used by the physician to deliverinterventional devices, such as a balloon angioplasty dilatationcatheter or a stent delivery catheter, into the area of treatment. Afterthe interventional procedure is completed, a recovery sheath can bedelivered over the guide wire using over-the-wire techniques to collapsethe expanded filter for removal from the patient's vasculature. Asmentioned above, the recovery device, i.e., the recovery sheath, shouldbe relatively flexible to track over the guide wire and to avoidstraightening the body vessel once it is in place.

When a combination of an expandable filter and guide wire is utilized,it is important that the expandable filter remains flexible in order tonegotiate the often tortuous anatomy through which it is beingdelivered. An expandable filter which is too stiff could prevent thedevice from reaching the desired deployment position within thepatient's vasculature. As a result, there is a need to increase theflexibility of the expandable filter without compromising its structuralintegrity once in position within the patient's body vessel.Additionally, a fluoroscope is currently the most widely used instrumentto visualize the filter during deployment and as such, requires anexpandable filter having sufficient radiopacity to produce anidentifiable image.

Expandable filters can be provided with high flexibility by forming thestruts of the filter assembly from relatively thin material. However,the use of thin material often can reduce the radiopacity of theexpandable filter, often making it difficult for the physician tovisualize the filter during deployment. Conversely, the use of thickermaterials, which can promote radiopacity of the expandable filter,usually reduces its flexibility, which may impair the deliverability ofthe expandable filter within the patient Since some expandable filterassemblies are made from nickel titanium alloys, which provide theself-expansion characteristics to the filter assembly, there may be aneed for increasing radiopacity since nickel titanium generally has alow degree of radiopacity. Moreover, the radiopacity of an expandablefiltering assembly which utilizes nickel titanium can be greatly reducedif the struts of the filter assembly are formed thinner in order toincrease the flexibility of the filter assembly. Therefore, there is aneed for a careful balance between achieving high flexibility in thefilter assembly while maintaining sufficient radiopacity to allow thedevice to be visualized using current visualization equipment.

What has been needed is an expandable filter assembly having highflexibility with sufficient strength and radiopacity to be successfullydeployed within a patient's vasculature to collect embolic debris whichmay be released into the patient's vasculature. The present inventiondisclosed herein satisfies these and other needs.

SUMMARY OF THE INVENTION

The present invention provides an expandable strut assembly and methodsfor making the same which can be used to create an embolic filteringdevice for capturing embolic debris created during the performance of atherapeutic interventional procedure, such as a balloon angioplasty orstenting procedure, in a body vessel. The present invention isparticularly useful when an interventional procedure is being performedin critical arteries, such as the carotid arteries, in which vitaldownstream blood vessels can easily become blocked with embolic debris,including the main blood vessels leading to the brain. The presentinvention provides the physician with a flexible embolic filteringdevice which is sufficiently flexible to be steered through tortuousanatomy, but yet possesses sufficient strength to hold open a filteringelement against the wall of the body vessel for capturing embolicdebris. Moreover, the present invention provides sufficient flexibilitywithout compromising the radiopacity characteristics of the filteringdevice. As a result, an embolic filtering device made in accordance withthe present invention is relatively easy to deploy, has enhancedvisibility under flouroscopy, and has good flexibility and conformableto the patient's anatomy.

An embolic filter assembly of the present invention utilizes anexpandable strut assembly made from a self-expanding material, forexample, nickel titanium (NiTi) or spring steel, and includes a numberof outwardly extending struts capable of expanding from a collapsedposition having a first delivery diameter to an expanded or deployedposition having a second implanted diameter. A filter element made froman embolic-capturing material can be attached to the expandable strutassembly to move between the collapsed position and the deployedposition with expandable struts.

The struts of the strut assembly can be set to remain in the expanded,deployed position until an external force is placed over the struts tocollapse and move the struts to the collapsed position. One way ofaccomplishing this is through the use of a restraining sheath, forexample, which can be placed over the filtering device in a coaxialfashion to contact the strut assembly and move the assembly into thecollapsed position. The embolic filtering device can be implanted in thepatient's vasculature and remain implanted for a period of time or canbe attached to the distal end of an elongated member, such as a guidewire, for temporary placement in the vasculature. A guide wire is usedin conjunction with the filtering device when embolic debris is to befiltered during an interventional procedure In this manner, the guidewire and filtering assembly, with the restraining sheath placed over thefilter assembly, can be placed into the patient's vasculature. Once thephysician properly manipulates the guide wire into the target area, therestraining sheath can be retracted to deploy the strut assembly intothe expanded position. This can be easily performed by the physician bysimply retracting the proximal end of the restraining sheath (locatedoutside of the patient). Once the restraining sheath is retracted, theself-expanding properties of the strut assembly cause each strut to movein a outward, radial fashion away from the guide wire to contact thewall of the body vessel. As the struts expand radially, so does thefilter element which will now be maintained in place to collect anyembolic debris that may be released into the bloodstream as thephysician performs the interventional procedure. The guide wire is usedby the physician to deliver the necessary interventional device into theare of treatment. The deployed filter element captures embolic debriswhich may be created and released into the body vessel during theprocedure.

The strut assembly which forms part of the filtering assembly includesportions in which the struts flex during delivery and recovery of thedevice within the patient's vasculature. Also, there are portions of thestrut assembly which will remain relatively stable (i.e., largelyundeformed or not flexed) during the travel through the sometimestortuous pathway of the patient's vasculature. For example, as theembolic filtering device is being delivered through the patient'svasculature, it will bend longitudinally in order to cross and navigatethe curves of the vasculature. When the strut assembly passes throughsuch curved portions of the vasculature, the flexing portions of thestrut assembly will resiliently flex while the stable portions remainlargely unflexed or undeformed, even when the filtering assembly as awhole is being delivered through extremely tight turns. Thus, the strutassembly of the embolic filtering assembly can be thought of having bothflexing portions and stable portions which cooperate with each other inorder to provide a composite assembly having both the necessaryflexibility and strength to create an effective embolic filteringdevice.

The flexibility of the strut assembly is largely derived from thoseportion of the struts which actually flex, without substantialassistance from the stable portions of the assembly Those stableportions are usually not subject to sufficient loads to cause bendingwhen the composite device is delivered across curved portions of theanatomy since the flexing portions delivering the flexibility need tonegotiate the turns. Accordingly, the stable portions of the strutassembly will remain substantially stiff and will not undergosubstantial bending or flexing. As a result, these stable portionsprovide strength to the strut assembly which will be later needed whenthe strut assembly is expanded in the body vessel to maintain the filterelement in its deployed position in the body vessel. Accordingly, thethickness or width of the stable portions of the strut assembly will notmaterially impact the overall flexibility or ease of delivering theembolic filtering assembly through the patient's vasculature.

The flexing portions of the strut assembly, on the other hand, can havereduced strut thickness or strut width to increase the strut assembly'soverall ability to flex or bend as it is being delivered through thecurved portions of the anatomy. Thus, in order to provide an optimalrange of strength, flexibility and radiopacity, the present inventionprovides a strut assembly having thinner areas which promoteflexibility, with greater strut thickness and/or widths in select stableareas to promote greater strength. This use of thicker and/or widerstruts provides enhanced visibility by increasing the radiopacity inthose select areas. By increasing the amount of material in the stableareas of the strut assembly, overall flexibility should not be impactedby the thicker or wider struts in the stable portions. On the otherhand, a thinner and/or narrower strut can be utilized in the flexingportions to achieve the needed overall flexibility for the strutassembly. Again, the stable portions could utilize thicker struts orwider struts for increased radiopacity while the thinner, narrowerstruts in the flexing portions would create preferential bending pointsleading to enhanced conformability and flexibility.

Additionally, in embolic filtering devices which utilize a restrainingsheath to deploy the self-expanding filter assembly, the surface area ofthe strut assembly in contact with the sheath can be decreased therebyreducing the amount of friction created between restraining sheath andstrut assembly as the sheath is being retracted over the struts. As aresult, it should be easier to retract the restraining sheath once thefilter assembly is to be deployed in the patient's vasculature. Thecombination of these properties lead to an embolic filtering devicewhich can be easy to deploy, is more visible under a fluoroscope, andhas increased flexibility and conformability with the patient's anatomy.The present invention is also directed to various methods for makingsuch an expandable strut assembly/filtering device.

It is to be understood that the present invention is not limited by theembodiments described herein. The present invention can be used inarteries, veins, and other body vessels. Other features and advantagesof the present invention will become more apparent from the followingdetailed description of the invention, when taken in conjunction withthe accompanying exemplary drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an embolic filtering device embodyingfeatures of the present invention.

FIG. 2 is an elevational view of the various components making up theembodiment of the embolic filtering device shown in FIG. 1.

FIG. 3 is an elevational view, partially in cross section, of an embolicfiltering device embodying features of the present invention as it isinitially being delivered past an area of treatment within a bodyvessel.

FIG. 4 is an elevational view, partially in cross section, similar tothat shown in FIG. 3, wherein the embolic filtering device is deployedin its expanded, implanted position within the body vessel.

FIG. 5 is an elevational view of the embolic filtering device of FIG. 1.

FIG. 6 is an elevational view of one embodiment of a strut assemblywhich can be used to form the embolic filtering device of FIGS. 1-4.

FIG. 7 is an elevational view, partially fragmented, of flexing portionsof the strut assembly shown in FIG. 6.

FIG. 8A is an elevational view, partially fragmented, of a strut portionhaving uniform thickness and width which has been used to form a part ofa strut assembly.

FIG. 8B is an elevational view, partially fragmented, of one embodimentof a strut portion made in accordance with the present invention thatcan be used to form part of the strut assembly.

FIG. 8C is an elevational view, partially fragmented, of anotherembodiment of a strut portion made in accordance with the presentinvention that can be used to form part of a strut assembly.

FIG. 8D is an elevational view, partially fragmented, of anotherembodiment of a strut portion made in accordance with the presentinvention that can be used to form a part of a strut assembly.

FIG. 9A is an elevational view of a tubular member used to form oneparticular embodiment of the present invention.

FIG. 9B is an elevational view of one particular strut pattern which canbe formed in the tubular member shown in FIG. 9A to create oneparticular embodiment of a strut assembly made in accordance with thepresent invention.

FIG. 9C is an elevational view which depicts the wall thickness of thestrut pattern shown in FIGS. 9A and 9B taken along line 9C-9C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings, in which like reference numerals representlike or corresponding elements in the drawings, FIGS. 1 and 2 illustrateone particular embodiment of an embolic filtering device 10incorporating features of the present invention. This embolic filteringdevice 10 is designed to capture embolic debris which may be created andreleased into a body vessel during an interventional procedure. Theembolic filtering device 10 includes an expandable filter assembly 12having a self-expanding strut assembly 14 and a filter element 16attached thereto. In this particular embodiment, the expandable filterassembly 12 is rotatably mounted on the distal end of an elongatedtubular shaft, such as a steerable guide wire 18. A restraining ordelivery sheath 20 (FIG. 3) extends coaxially along the guide wire 18 inorder to maintain the expandable filter assembly 12 in its collapsedposition until it is ready to be deployed within the patient'svasculature. The expandable filter assembly 12 is deployed by thephysician by simply retracting the restraining sheath 20 proximally toexpose the expandable filter assembly. The self-expanding strut assembly14 thus becomes uncovered and immediately begins to expand within thebody vessel (see FIG. 4).

It should be appreciated that the embolic filtering device 10 depictedherein is just one example of the numerous designs which can be used tocreate an embolic protection device made in accordance with the presentinvention. An obturator 22 affixed to the distal end of the filterassembly 12 can be implemented to prevent possible “snowplowing” of theembolic protection device as it is being delivered through thevasculature. The obturator can be made from a soft polymeric material,such as Pebax D 40, and has a smooth surface to help the embolicfiltering device travel through the vasculature and cross lesions whilepreventing the distal end of the restraining sheath 20 from “digging” or“snowplowing” into the wall of the body vessel. Additional detailsregarding the particular structure and shape of the various elementsmaking up the filter assembly 12 are provided below.

In FIG. 3, the embolic filtering device 10 is shown as it is beingdelivered within an artery 24 or other body vessel of the patient. Thisportion of the artery 24 has an area of treatment 26 in whichatherosclerotic plaque 28 has built up against the inside wall 30 of theartery 24. The filter assembly 12 is to be placed distal to, anddownstream from, the area of treatment 26 as is shown in FIGS. 3 and 4.The therapeutic interventional procedure may comprise the implantationof a stent (not shown) to increase the diameter of an occluded arteryand increase the flow of blood therethrough. It should be appreciatedthat the embodiments of the embolic filtering device and method formanufacturing and using the same are illustrated and described herein byway of example only and not by way of limitation. Also, while thepresent invention is described in detail as applied to an artery of thepatient, those skilled in the art will appreciate that it can also beused in other body vessels, such as the coronary arteries, carotidarteries, renal arteries, saphenous vein grafts and other peripheralarteries. Additionally, the present invention can be utilized when aphysician performs any one of a number of interventional procedures,such as balloon angioplasty, laser angioplasty or atherectomy whichgenerally require an embolic filtering device to capture embolic debriscreated during the procedure.

The strut assembly 14 includes self-expanding struts 32 which, uponrelease from the restraining sheath 20, expand the filter element 16into its deployed position within the artery (FIG. 4). When the struts32 are expanded, the filter element 16 may take on a basket shape, orany other shape, that will adequately deploy the filter element 16against the wall of the artery. Embolic debris created during theinterventional procedure and released into the bloodstream are capturedwithin the deployed filter element 16. Although not shown, a balloonangioplasty catheter can be initially introduced within the patient'svasculature in a conventional SELDINGER technique through a guidingcatheter (not shown). The guide wire 18 is disposed through the area oftreatment and the dilatation catheter can be advanced over the guidewire 18 within the artery 24 until the balloon portion is directly inthe area of treatment 26. The balloon of the dilatation catheter can beexpanded, expanding the plaque 28 against the inside wall 30 of theartery 24 to expand the artery and reduce the blockage in the vessel atthe position of the plaque 28. After the dilatation catheter is removedfrom the patient's vasculature, a stent (not shown) could be implantedin the area of treatment 26 using over-the-wire techniques to help holdand maintain open this portion of the artery 24 and help preventrestenosis from occurring in the area of treatment. The stent could bedelivered to the area of treatment on a stent delivery catheter (notshown) which is advanced from the proximal end of the guide wire to thearea of treatment. Any embolic debris created during the interventionalprocedure will be released into the bloodstream and should enter thefilter 16. Once the procedure is completed, the interventional device isremoved from the guide wire and the filter assembly 14 is to becollapsed and removed from the artery 24, taking with it any embolicdebris trapped within the filter element 16. A recovery sheath (notshown) can be delivered over the guide wire 18 to collapse the filterassembly for removal from the patient's vasculature.

The ability of the embolic filtering device to negotiate the sometimetortuous anatomy of the patient results from the flexibility associatedwith the strut assembly 14 which forms part of the filter assembly 12.Referring specifically now to FIGS. 6 and 7, one particular embodimentof a strut assembly 14 is shown which incorporates features of thepresent invention. It should be appreciated by those skilled in the artthat this is just one particular structure incorporating struts whichform a basket-like structure that can be used in accordance with thepresent invention. Many other structural designs could also beimplemented to create the strut assembly without departing from thespirit and scope of the present invention.

The struts 32 which form the strut assembly 14 shown in FIGS. 6 and 7include flexing portions 36 in which the struts or portions of thestruts flex or otherwise resiliently bend both during delivery andrecovery of the embolic filtering device. Also, there are stableportions 38 of the strut assembly which remain stable (i.e., largelyundeformed or unflexed) during delivery through the vasculature. Forexample, as the embolic filtering device is being delivered through thepatient's vasculature, it will bend longitudinally to cross and navigatethe curves of the vasculature. When the strut assembly passes throughsuch curved portions, the flexing portions 36 of the assembly will flexwhile the remaining portions stay relatively unflexed or stiff, even asthe filtering assembly as a whole is bent through extremely tight turns.The flexing portions 36 and stable portions 38 thus cooperate with eachother in order to provide the necessary flexibility to bend and bedelivered through tight turns. The strength of the strut assembly 14 isachieved by the stable portions 38 once the strut assembly is deployedin the body vessel.

The flexibility of the strut assembly 14 is largely derived from theflexing portions 36 of the strut, without substantial assistance fromthe stable portions 38 of the assembly, even though stable portions 38are subjected to some bending forces when the device is being deliveredacross curved portions of the anatomy. Accordingly, the stable portions38 will remain substantially straight and will not undergo substantialbending or flexing. These stable portions 38 do have sufficient strengthto provide the structural integrity needed to maintain the filterassembly 12 in its expanded position once placed in the artery. Thestrong stable portions 38 also provide additional metal to the strutassembly which allows the embolic filtering device 10 to become morevisible utilizing equipment, such as a fluoroscope, to determine thelocation of the device within the patient's anatomy. As can be seen inFIGS. 6 and 7, the stable portions 38 include strut portions which havegreater strut depth or thickness than the portion of the struts whichare located in the flex portions 36. As can be seen specifically in FIG.7, the thickness of the strut or the strut depth is the measurement ofthe strut from the inner surface 40 to the outer surface 42 of thestrut. In FIG. 7, arrows T₁ show the greater strut thickness in thestable portions 38 which provides the higher strength and radiopacitythan the strut thickness in the flex portions 36 (indicated by arrowsT₂). The strut thickness in the flex portions 38 depicted by arrows T₂is less than the strut thickness in the stable portion 36, thusproviding increased flexibility to the strut assembly 14.

The stable portion 38 may also include struts which have greater strutwidths than the struts which are located in the flexing portions 36 ofthe strut assembly 14. In FIG. 7, arrows W₁ show the wider strut formedin the stable portions 38. Arrows W₂ show the smaller strut widthsappearing in the flexing portions 36. The smaller strut width providesgreater flexibility, enhancing the ability of the strut assembly 14 tonegotiate the tortuous anatomy of the patient. As a result, the flexingportions 36 may include both smaller strut thickness and a smaller strutwidth to provide this increased flexibility. The flexing portions can bethought of somewhat as mechanical hinges which provide regions ofarticulation to the strut assembly. Conversely, the stable portions 38may include struts having greater strut thickness, and strut width toprovide additional strength and added mass to increase the level ofradiopacity of the strut assembly 14. As is shown in FIG. 6, there areseveral areas in which flexing portions 36 are located to provide theincreased flexibility needed to maneuver in the patient's vasculature.It should be appreciated that the number, size and location of flexingportions 36 and stable portions 38 of the strut assembly 14 will varydepending upon the particular structure utilized to create the strutassembly.

The current invention provides additional strut thickness and/or widthto all or part of the stable portions of the strut assembly. FIGS. 8A-8Ddepicts a partially fragmented perspective view of a portion of a strutsimilar to that shown in FIGS. 6 and 7 which shows different ways ofincreasing the mass of the strut in the stable portion of the strutassembly. In FIG. 8A, it can be seen that all portions of the strut 44have the same, or a nominal strut depth 46 and a constant strut width48. In the embodiment shown in FIG. 8A, there are no stable portions orflex portions due to the fact that the nominal thickness 46 and nominalstrut width 48 are substantially uniform throughout. Many prior artfiltering devices are made with struts having uniform strut thicknessand width. Bending occurs on those devices at points along the strutassembly which are most vulnerable to bending forces. In such devices,there are no specifically formed flexible struts which are designed toflex and bend and take the brunt of the bending forces that can begenerated during passage of the device through the patient'svasculature. In FIG. 8B, however, the strut pattern 50 has both stableportions 38 and flexing portions 36. The stable portion 38 is made witha material which has greater than nominal depth 52 and greater thannominal width 54 without compromising the flexibility of the struts inthe flexing portion 36. When used on the strut assembly, these thickerand wider struts in the stable portions 38 provide additional strengthand enhanced radiopacity characteristics to the strut assembly 14. FIG.8C depicts a further embodiment of stable portions 38 of a strut 56having varying strut thickness which smoothly transitions from a nominalstrut thickness 46 to a greater-than-nominal thickness 52. In theparticular embodiment of FIG. 8C, the strut width 58 is substantiallythe same. However, due to the greater than nominal strut thickness 52 inthe stable portions 38, additional strength and increased radiopacitywill be provided to the strut assembly. FIG. 8D provides still anotherembodiment of a strut portion 60 of a strut assembly in which uniquestable portions 38 can be found. In this particular embodiment, thestable portion 38 is made from a geometry which includes a “bump”pattern generating a greater-than-nominal strut thickness 52 in adesired area. The bumps 62 formed in the stable portions 38 would beinherent in the material used to create the strut assembly. Also, in theembodiments shown in FIGS. 8C and 8D, when a restraining sheath isutilized to deploy and retrieve the filter assembly, the variablethickness design effectively reduces the surface area of the strut incontact with sheath, thereby reducing frictional forces which can begenerated as the restraining sheath moves over the strut assembly. As aresult, the restraining sheath should slide off of the strut assemblywith less resistance.

The preparation of a strut assembly in accordance with the presentinvention can be accomplished in a variety of ways. An initial stepwould be to select a particular pattern for the struts and identifystable portions and flexing portions. The identification of stableportions can be accomplished using many different techniques. Forexample, a computer base modeling of a strut pattern can be performedthat models the embolic protection device during bending of the strutassembly. Alternatively, a physical model or actual embolic protectiondevice bearing the particular strut pattern could be prepared andsubject to bending, so that flexing and stable portions of the strutassembly could be identified through inspection of the physical device.Other approaches for identifying the flexing portions and stableportions would be well-known in the art and are within the scope of thepresent invention.

After identification of the stable and flexing portions has occurred, astrut assembly can be prepared having the desired strut pattern, withthe variations in the strut thickness and/or strut widths associatedwith the flexing portions and stable portions. Various techniques couldbe utilized to manufacture the strut assembly. For example, the strutassembly could be prepared from a tubular member having a nominalthickness with the strut pattern being laser cut or otherwise cut tocreate a rough pattern. Additional material could then be added to thesurface of the cut strut pattern on selected stable portions until theselected stable portions reach the desired greater-than-nominal strutdepth or greater-than-nominal width, depending again, on the particularpattern which is to be utilized. Various techniques could be used to addthe additional material, including sputter coating, electroplating, orchemical vapor deposition.

Referring now to FIGS. 9A-9C, a particular strut pattern 66 which formsthe strut assembly 14, is depicted two-dimensionally (FIG. 9B) as if thestrut assembly 14 were cut longitudinally and “unrolled” to form a flatsheet, showing the combination of flex portions 36 and stable portions38 which, in combination, create the strut assembly 14. FIG. 9A shows across-sectional view of a tubular member 68 which could be utilized andlaser cut in order to create the varying strut thicknesses of the strutassembly shown in FIG. 9B. As is shown, the tubular member 68 hasdifferent wall thicknesses which correspond to the flexing portions 36and stable portions 38 of the strut assembly 14. The areas 70 which havelarger-than-nominal strut thickness in the tubular member are utilizedto create the stable regions 38 of the strut assembly. As can be seen inFIGS. 9A and 9C, the wall thicknesses in the areas forming the stableregions 38 can vary. For example, areas 70 have the same wall thicknessT₁. However, the wall thickness T₃ in area 72 forming another stableregion has an even greater wall thickness than area 70. This creates aneven larger strut thickness in those stable regions of the strutassembly. Area 74, which forms the flexing portions of the strutassembly, has a wall thickness T₂ which is less than T₁ and T₃.Moreover, the width can be increased in those regions as well. In asimilar fashion, the strut widths and strut depths in the flexingregions can vary on the strut assembly as well. For example, as can beseen in FIG. 9B, certain strut widths in flexing portions 76 are smallerthan the strut widths in the other flexing portions 36. The strutthickness in these areas could also be less-than-nominal strut thicknessto provide even increased flexibility. Moreover, the flexing portionscan have varying strut thickness, similar to the varying strut thicknessof the stable portions 38 depicted in FIG. 8C. The free ends of thestruts could be attached to collars 31, as is shown in FIG. 6, whichhelp form the particular shape of the strut assembly disclosed herein.The free ends 78 of the struts could be attached to the collars usingwell-known bonding techniques known in the art, including welding,brazing, and adhesive bonding. It should be appreciated that numerousvariations of strut width and depths in the various stable and flexingportions of the strut assembly can be achieved in accordance with thepresent invention.

Due to manufacturing and other considerations, it may be desireable tostart with a tubular member having a desired larger than nominalthickness, and then selectively reduce the thickness of desiredportions, such as the flexing portions, to create a nominal thickness oreven a less-than-nominal thickness. In this particular manner, thetubular member shown in FIG. 9A would have a greater-than-nominalthickness and selected portions of the outer surface would be removed tocreate the nominal thickness utilized to create the flexing portions ofthe strut assembly. In the embodiment shown in FIG. 9A, the machiningcould involve rotating the tubular member along its longitudinal axis,as may be accomplished utilizing a lathe or other rotating device, andpressing a machine tool against the outer surface. Other techniquesinclude chemical etching, laser ablation, grinding, or milling. Once theparticular form of the tubular member is selected, the pattern whichforms the strut assembly could then be cut into the tubular member. Inthis manner, the width of the struts in the stable portions could be cutto be larger than the struts in the flexing portions, as is shown inFIG. 9B. Any one of a number of different combinations of stableportions and flexing portions can be utilized, as will be appreciated bythose skilled in the art, to create the particular pattern for the strutassembly. Accordingly, a strut assembly will have flexing portionshaving a nominal thickness and/or nominal strut width, with stableportions having greater than nominal thickness and/or greater thannominal strut widths.

In addition to the physical machining methods discussed above, thereduction in strut thickness could also be achieved through a variety ofother methods, including ablating selected surface areas. The ablationcould be formed through various methods, including chemical and/or laserablation. This step may also be formed as part of the process of cuttingthe strut pattern into the tubular member. For example, where lasercutting is used to cut the strut pattern, the laser might also be usedto thin desired portions of the tubular member. Such thining using alaser might involve changing the focus depth of the laser, changinglaser power, or using the laser to tangentially “shave” across thesurface of the tubular member thereby removing a layer of material.

The strut assembly of the present invention can be made in many ways.However, the one particular method of making the strut assembly is tocut a thin-walled tubular member, such as nickel-titanium hypotube, toremove portions of the tubing in the desired pattern for each strut,leaving relatively untouched the portions of the tubing which are toform each strut. The tubing may be cut into the desired pattern by meansof a machine-controlled laser. Prior to laser cutting the strut pattern,the tubular member could be formed with varying wall thicknesses whichwill be used to create the stable and flexing portions of the strutassembly.

The tubing used to make the strut assembly could possible be made ofsuitable biocompatible material such as stainless steel. The stainlesssteel tube may be alloy-type: 316L SS, Special Chemistry per ASTMF138-92 or ASTM F139-92 grade 2. Special Chemistry of type 316L per ASTMF138-92 or ASTM F139-92 Stainless Steel for Surgical Implants in weightpercent.

The strut size is usually very small, so the tubing from which it ismade must necessarily also have a small diameter. Typically, the tubinghas an outer diameter on the order of about 0.020-0.040 inches in theunexpanded condition. The greater-than-nominal wall thickness of thetubing is usually about 0.076 mm (0.003-0.006 inches). As can beappreciated, the nominal strut depth in the flexing portions will beless. For strut assemblies implanted in body lumens, such as PTAapplications, the dimensions of the tubing may be correspondinglylarger. While it is preferred that the strut assembly be made from lasercut tubing, those skilled in the art will realize that the strutassembly can be laser cut from a flat sheet and then rolled up in acylindrical configuration with the longitudinal edges welded to form acylindrical member.

Generally, the hypotube is put in a rotatable collet fixture of amachine-controlled apparatus for positioning the tubing relative to alaser. According to machine-encoded instructions, the tubing is thenrotated and moved longitudinally relative to the laser which is alsomachine-controlled. The laser selectively removes the material from thetubing by ablation and a pattern is cut into the tube. The tube istherefore cut into the discrete pattern of the finished struts. Thestrut assembly can thus be laser cut much like a stent is laser cut.Details on how the tubing can be cut by a laser are found in U.S. Pat.No. 5,759,192 (Saunders) and U.S. Pat. No. 5,780,807 (Saunders), whichhave been assigned to Advanced Cardiovascular Systems, Inc.

The process of cutting a pattern for the strut assembly into the tubinggenerally is automated except for loading and unloading the length oftubing. For example, a pattern can be cut in tubing using a CNC-opposingcollet fixture for axial rotation of the length of tubing, inconjunction with CNC X/Y table to move the length of tubing axiallyrelative to a machine-controlled laser as described. The entire spacebetween collets can be patterned using the CO₂ or Nd:YAG laser set-up.The program for control of the apparatus is dependent on the particularconfiguration used and the pattern to be ablated in the coding.

A suitable composition of nickel-titanium which can be used tomanufacture the strut assembly of the present invention is approximately55% nickel and 45% titanium (by weight) with trace amounts of otherelements making up about 0.5% of the composition. The austenite finishtransformation temperature is between about 0° C. and 20° C. in order toachieve superelasticity. The austenite finish temperature is measured bythe bend and free recovery tangent method. The upper plateau strength isabout a minimum of 60,000 psi with an ultimate tensile strength of aminimum of about 155,000 psi. The permanent set (after applying 8%strain and unloading), is approximately 0.5%. The breaking elongation isa minimum of 10%. It should be appreciated that other compositions ofnickel-titanium can be utilized, as can other self-expanding alloys, toobtain the same features of a self-expanding stent made in accordancewith the present invention.

The strut assembly of the present invention can be laser cut from a tubeof nickel-titanium (Nitinol) whose transformation temperature is belowbody temperature. After the strut pattern is cut into the hypotube, thetubing is expanded and heat treated to be stable at the desired finaldiameter. The heat treatment also controls the transformationtemperature of the strut assembly such that it is super elastic at bodytemperature. The transformation temperature is at or below bodytemperature so that the stent is superelastic at body temperature. Thestrut assembly is usually implanted into the target vessel which issmaller than the diameter if the strut assembly in the expanded positionso that the struts apply a force to the vessel wall to maintain thefilter element in the expanded position. It should be appreciated thatthe strut assembly can be made from either superelastic, stress-inducedmartensite NiTi or shape-memory NiTi.

One way of making the strut assemblies of the present device is toutilize a shape-memory material, such as nickel titanium, which has thestruts cut utilizing a machine-controlled laser. A tubular piece ofmaterial could be utilized in this process. The strut assembly could bemanufactured to remain in its open position while at body temperatureand would move to its collapsed position upon application of a lowtemperature. One suitable method to allow the strut assembly to assume aphase change which would facilitate the strut and filter assembly beingmounted into the restraining sheath include chilling the filter assemblyin a cooling chamber maintained at a temperature below the martensitefinish temperature through the use of liquid nitrogen. Once the strutassembly is placed in its collapsed state, the restraining sheath can beplaced over the device to prevent the device from expanding once thetemperature is brought up to body temperature. Thereafter, once thedevice is to be utilized, the restraining sheath is simply retracted toallow the filter assembly/strut assembly to move to its expandedposition within the patient's vasculature. If superelastic NiTi is used,the strut assembly/filter assembly can be simply back loaded into therestraining sheath. The strut assembly would be “set” to the expandedposition.

The polymeric material which can be utilized to create the filteringelement include, but is not limited to, polyurethane and Gortex, acommercially available material. Other possible suitable materialsinclude ePTFE. The material can be elastic or non-elastic. The wallthickness of the filtering element can be about 0.00050-0.0050 inches.The wall thickness may vary depending on the particular materialselected. The material can be made into a cone or similarly sized shapeutilizing blow-mold technology. The perfusion openings can be anydifferent shape or size. A laser, a heated rod or other process can beutilized to create to perfusion openings in the filter material. Theholes, would of course be properly sized to catch the particular size ofembolic debris of interest. Holes can be lazed in a spiral pattern withsome similar pattern which will aid in the re-wrapping of the mediaduring closure of the device. Additionally, the filter material can havea “set” put in it much like the “set” used in dilatation balloons tomake the filter element re-wrap more easily when placed in the collapsedposition.

The materials which can be utilized for the restraining sheath andrecovery sheath can be made from polymeric material such as cross-linkedHDPE. These sheaths can alternatively be made from a material such aspolyolifin which has sufficient strength to hold the compressed strutassembly and has relatively low frictional characteristics to minimizeany friction between the filtering assembly and the sheath. Friction canbe further reduced by applying a coat of silicone lubricant, such asMicroglide®, to the inside surface of the restraining sheath before thesheaths are placed over the filtering assembly.

Further modifications and improvements may additionally be made to thedevice and method disclosed herein without departing from the scope ofthe present invention. Accordingly, it is not intended that theinvention be limited, except as by the appended claims.

1. An embolic filtering device for filtering embolic debris from apatient's vasculature, comprising: a filtering assembly including anexpandable strut assembly and a filter element attached thereto; whereinthe strut assembly is adapted to move between a collapsed position andan expanded position and has flexing portions which flex when subjectedto bending forces when the filtering assembly is in the collapsedposition and stable portions connected by flexing portions, the stableportions remaining relatively stiff when the filtering assembly is inthe collapsed position while the flexing portions provide three degreesof freedom flexing between stable portions when the filtering assemblyis placed in the collapsed position, wherein the stable portions includestruts, each strut having a strut width and a strut thickness, and theflexing portions include struts, each strut having strut width and astrut thickness, the strut width and thickness of the struts of theflexing portions being less than the strut width and strut thickness ofthe stable portions.
 2. The filtering device of claim 1, furtherincluding an elongated member having a proximal end and a distal end,the filtering assembly being mounted near the distal end, the elongatedmember being steerable to place the filtering assembly in the desiredposition within the patient's vasculature.
 3. The filtering device ofclaim 1, wherein flexing portions interconnect adjacent stable portions.4. The filtering device of claim 1, wherein the flexing portions undergolittle or no deformation when subjected to bending forces developedduring passage through the patient's vasculature to help maintain theshape of the expanded strut assembly once expanded.
 5. The filteringdevice of claim 4, wherein the flexing portions of the strut assemblyare made from a material which is self-expanding.
 6. The filteringdevice of claim 1, wherein the strut assembly is made from a materialwhich is self-expanding.
 7. The filtering device of claim 6, wherein thematerial is nickel-titanium.
 8. The filtering device of claim 6, whereinthe flexing portions of the strut assembly enhance the movement of thestrut assembly between the first collapsed position and the seconddelivery position.
 9. The filtering device of claim 1, wherein the strutassembly is made from a plurality of struts, each strut having an insidesurface and an outside surface which define a strut thickness, the strutthickness in the stable portions being generally greater than the strutthickness in the flexing portions of the strut assembly.
 10. Thefiltering device of claim 9, wherein the strut thickness in the flexingportions define a nominal strut thickness and the strut thickness in thestable portions define a greater-than-nominal strut thickness.
 11. Thefiltering device of claim 10, wherein some of the flexing portions haveless than nominal strut thickness.
 12. The filtering device of claim 10,wherein some flexing portions have strut thickness different from otherflexing portions but less than the strut thickness in the stableportions.
 13. The filtering device of claim 9, wherein each strut has aparticular strut width, the strut widths in the stable portions beinggenerally greater than the strut widths in the flexing portions.
 14. Thefiltering device of claim 1, wherein the strut assembly is formed from aplurality of struts, each strut having a particular strut width, thestrut widths in the stable portions being generally greater than thestrut widths in the flexing portions of the strut assembly.
 15. Thefiltering device of claim 14, wherein the strut widths in the flexingportions define a nominal strut width and the strut width in the stableportions define a greater-than-nominal strut width.
 16. The filteringdevice of claim 1, wherein the flexing portions of the strut assemblyenhance the movement of the strut assembly between the first collapsedposition and the second delivery position.
 17. An embolic filteringdevice for filtering embolic debris from a patient's vasculature,comprising: a filtering assembly including an expandable strut assemblyand a filter element attached thereto, the strut assembly being adaptedto move between a first collapsed position and an expanded position andbeing formed from a plurality of struts arranged to create a desiredcomposite strut structure, each strut having an inner surface and anouter surface which defines a particular strut thickness and a strutwidth, wherein: portions of the composite strut assembly have strutthickness and strut width which are less than the strut thickness andstrut width of the remaining struts forming the strut assembly to impartflexibility to the composite strut assembly to allow the strut assemblyto resiliently flex while being delivered through the patient'svasculature.
 18. The filtering device of claim 17, further including anelongated member having a proximal end and a distal end, the filteringassembly being mounted near the distal end, the elongated member beingsteerable to place the filtering assembly in the desired position withinthe patient's vasculature.
 19. The filtering device of claim 17, whereinthe portions of the composite strut assembly having smaller strutthickness undergo little or no deformation when subjected to bendingforces developed during delivery of the filtering assembly through thepatient's vasculature to help maintain the shape of the expanded strutassembly once expanded.
 20. The filtering device of claim 17, whereinthe portions of the composite strut assembly having smaller strutthickness enhances the movement of the strut assembly between thecollapsed position and the expanded position.
 21. An embolic filteringdevice for filtering embolic debris from a patient's vasculature,comprising: a filtering assembly including an expandable strut assemblyand a filter element attached thereto, the strut assembly being adaptedto move between a collapsed position and an expanded position and beingformed from a plurality of struts arranged to create a desired compositestrut structure, each strut having at least one flexing portion formedon the strut which exhibits more flexibility than the remaining portionof the strut, the flexing portion being located on each strut such thatwhen the strut assembly is placed in the collapsed position the flexingportions are placed substantially adjacent to each other to create acomposite flexing region on the strut assembly, wherein the strutassembly include struts, each strut having a strut width and a strutthickness, the width and thickness of the struts of the flexing portionsbeing less than the strut width and strut thickness in the remainingportion of the strut assembly.
 22. The filtering device of claim 21,wherein each strut of the strut assembly has an inside surface and anoutside surface which define the strut thickness, the strut thickness inthe flexing portions being generally less than the strut thickness inthe remaining portion of the strut.
 23. The filtering device of claim21, wherein each strut has a particular strut width and the strut widthsin the flexing portions are generally less than the strut width in theremaining portion of the strut.
 24. The filtering device of claim 21,wherein each strut has a substantially uniform width and wall thicknessalong the length of the strut except for the flexing portions formed oneach strut.
 25. The filtering device of claim 21, wherein some of thestruts have a plurality of flexing portions formed on the strut.
 26. Thefiltering device of claim 25, wherein the struts having a plurality offlexing portions include at least two flexing portions having differentstrut widths or wall thicknesses from each other.
 27. An embolicfiltering device for filtering embolic debris from a patient'svasculature, comprising: a filtering assembly including an expandablestrut assembly and a filter element attached thereto, the strut assemblybeing adapted to move between a collapsed position and an expandedposition and having a longitudinal length and non-uniform mass along itslongitudinal length, the strut assembly having a flexing region formedtherein and a stable region forming the remaining portion of the strutassembly, the flexing region having less mass than the stable region toprovide greater flexibility than the stable region of the strutassembly, the flexing region being arranged to create a hinge-likestructure to allow the strut assembly to bend at the flexing region whenthe strut assembly is placed in the collapsed position, wherein thestrut assembly is formed from a plurality of struts, each strut having aparticular strut width and wall thickness, the width and wall thicknessof the portion of each strut forming the flexing region of the strutassembly being less than the width and wall thickness of the strutsforming the stable region.
 28. The filtering device of claim 27, whereinthe strut assembly has a plurality of flexing regions formed therein.29. The filtering device of claim 27, wherein the strut assembly isformed from a plurality of struts, each strut having an area of reducedmass along the strut length which forms the flexing portion of the strutassembly.